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  • 1995-1999  (4)
  • 1985-1989  (2)
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  • 1
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    Relationship of the time course of venous gas bubbles to altitude decompression illness (1996)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The correlation is low between the occurrence of gas bubbles in the pulmonary artery, called venous gas emboli (VGE), and subsequent decompression illness (DCI). The correlation improves when a "grade" of VGE is considered; a zero to four categorical classification based on the intensity and duration of the VGE signal from a Doppler bubble detector. Additional insight about DCI might come from an analysis of the time course of the occurrence of VGE. Using the NASA Hypobaric Decompression Sickness Databank, we compared the time course of the VGE outcome between 322 subjects who exercised and 133 Doppler technicians who did not exercise to evaluate the role of physical activity on the VGE outcome and incidence of DCI. We also compared 61 subjects with VGE and DCI with 110 subjects with VGE but without DCI to identify unique characteristics about the time course of the VGE outcome to try to discriminate between DCI and no-DCI cases. The VGE outcome as a function of time showed a characteristic short lag, rapid response, and gradual recovery phase that was related to physical activity at altitude and the presence or absence of DCI. The average time for DCI symptoms in a limb occurred just before the time of the highest fraction of VGE in the pulmonary artery. It is likely, but not certain, that an individual will report a DCI symptom if VGE are detected early in the altitude exposure, the intensity or grade of VGE rapidly increases from a limb region, and the intensity or grade of VGE remains high.
    Keywords: Aerospace Medicine
    Type: Undersea & hyperbaric medicine : journal of the Undersea and Hyperbaric Medical Society, Inc (ISSN 1066-2936); Volume 23; 3; 141-9
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    NASA TECHNICAL REPORTS
  • 2
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    Testing of hypotheses about altitude decompression sickness by statistical analyses (1996)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: This communication extends a statistical analysis of forced-descent decompression sickness at altitude in exercising subjects (J Appl Physiol 1994; 76:2726-2734) with a data subset having an additional explanatory variable, rate of ascent. The original explanatory variables for risk-function analysis were environmental pressure of the altitude, duration of exposure, and duration of pure-O2 breathing before exposure; the best fit was consistent with the idea that instantaneous risk increases linearly as altitude exposure continues. Use of the new explanatory variable improved the fit of the smaller data subset, as indicated by log likelihood. Also, with ascent rate accounted for, replacement of the term for linear accrual of instantaneous risk by a term for rise and then decay made a highly significant improvement upon the original model (log likelihood increased by 37 log units). The authors conclude that a more representative data set and removal of the variability attributable to ascent rate allowed the rise-and-decay mechanism, which is expected from theory and observations, to become manifest.
    Keywords: Aerospace Medicine
    Type: Undersea & hyperbaric medicine : journal of the Undersea and Hyperbaric Medical Society, Inc (ISSN 1066-2936); Volume 23; 4; 225-33
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    NASA TECHNICAL REPORTS
  • 3
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    Modeling the effects of exercise during 100% oxygen prebreathe on the risk of hypobaric decompression sickness (1997)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: BACKGROUND: Several previous studies indicated that exercise during prebreathe with 100% O2 decreased the incidence of hypobaric decompression sickness (DCS). We report a meta-analysis of these investigations combined with a new study in our laboratory to develop a statistical model as a predictive tool for DCS. HYPOTHESIS: Exercise during prebreathe increases N2 elimination in a theoretical 360-min half-time compartment decreasing the incidence of DCS. METHODS: A dose-response probability tissue ratio (TR) model with 95% confidence limits was created for two groups, prebreathe with exercise (n = 113) and resting prebreathe (n = 113), using nonlinear regression analysis with maximum likelihood optimization. RESULTS: The model predicted that prebreathe exercise would reduce the residual N2 in a 360-min half-time compartment to a level analogous to that in a 180-min compartment. This finding supported the hypothesis. The incidence of DCS for the exercise prebreathe group was significantly decreased (Chi-Square = 17.1, p 〈 0.0001) from the resting prebreathe group. CONCLUSIONS: The results suggested that exercise during prebreathe increases tissue perfusion and N2 elimination approximately 2-fold and markedly lowers the risk of DCS. Based on the model, the prebreathe duration may be reduced from 240 min to a predicted 91 min for the protocol in our study, but this remains to be verified. The model provides a useful planning tool to develop and test appropriate prebreathe exercise protocols and to predict DCS risks for astronauts.
    Keywords: Aerospace Medicine
    Type: Aviation, space, and environmental medicine (ISSN 0095-6562); Volume 68; 3; 199-204
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  • 4
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    Role of metabolic gases in bubble formation during hypobaric exposures (1998)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Our hypothesis is that metabolic gases play a role in the initial explosive growth phase of bubble formation during hypobaric exposures. Models that account for optimal internal tensions of dissolved gases to predict the probability of occurrence of venous gas emboli were statistically fitted to 426 hypobaric exposures from National Aeronautics and Space Administration tests. The presence of venous gas emboli in the pulmonary artery was detected with an ultrasound Doppler detector. The model fit and parameter estimation were done by using the statistical method of maximum likelihood. The analysis results were as follows. 1) For the model without an input of noninert dissolved gas tissue tension, the log likelihood (in absolute value) was 255.01. 2) When an additional parameter was added to the model to account for the dissolved noninert gas tissue tension, the log likelihood was 251.70. The significance of the additional parameter was established based on the likelihood ratio test (P 〈 0.012). 3) The parameter estimate for the dissolved noninert gas tissue tension participating in bubble formation was 19. 1 kPa (143 mmHg). 4) The additional gas tissue tension, supposedly due to noninert gases, did not show an exponential decay as a function of time during denitrogenation, but it remained constant. 5) The positive sign for this parameter term in the model is characteristic of an outward radial pressure of gases in the bubble. This analysis suggests that dissolved gases other than N2 in tissues may facilitate the initial explosive bubble-growth phase.
    Keywords: Life Sciences (General)
    Type: Journal of applied physiology (Bethesda, Md. : 1985) (ISSN 8750-7587); Volume 84; 3; 1088-95
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  • 5
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    Effect of Hydration on Nitrogen Washout in Humans (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Series of experiments described in NASA technical memorandum showed drinking water before breathing nearly pure oxygen has little or no effect on rate of removal of nitrogen from body. Experiments undertaken because data from some earlier experiments suggested that, under some conditions, hydration might help prevent decompression sickness.
    Keywords: LIFE SCIENCES
    Type: MSC-20686 , NASA Tech Briefs (ISSN 0145-319X); 9; 1; P. 113
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  • 6
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    Pulmonary hemodynamics, extravascular lung water and residual gas bubbles following low dose venous gas embolism in dogs (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Aviation, Space, and Environmental Medicine (ISSN 0095-6562); 60; 1178-118
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